This Question: 4 pts 23 of 25 (23 complete) is Quiz: 114 pts p... Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation 8p + x= 1400. Determine the rate at which sales are changing at a time when x = 20, p =5, and the price is falling at the rate of $.80 per week. The rate at which sales are changing is thousand units per week